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Quantum Dots Suitable for Computing

Photonics Spectra
Jan 2001
Kevin Robinson

A new study has found that quantum dots not only behave according to the predictions of quantum physics, but do so at room temperature. The discovery, which proves that the emission of quantum dots is binary in nature, brings closer the ability to harness these "artificial atoms" for computing applications.

Researchers at the University of California created CdSe/ZnS quantum dots using high-temperature organometallic processes. They dissolved the dots in hexane and spun-cast them on a glass coverslip, thus separating them by an average of 1 µm. They passed a polarized, 488-nm argon-ion laser beam through a high-NA objective on a confocal microscope and onto the coverslip to generate electron hole pairs in the quantum dots.

The same objective collected the resulting photoluminescence, which passed through an excitation beamsplitter and a holographic notch filter that blocked the scattered light. They then split the emission using a 50/50 nonpolarizing beamsplitter and focused it on the active areas of two single-photon-counting avalanche photodiodes.

To measure a single quantum dot, the scientists positioned the objective over a single bright spot, roughly 300 nm in diameter. They found that a dead time exists between the photon emissions from a dot, corresponding to the time it takes for its energy level to rise again to the excited state. What surprised everyone was that the phenomenon occurred in an uncooled setup.

Dots in Computers

The ability of quantum dots to be either on or off corresponds directly to the binary system of ones and zeros used in everyday computers. Proving that a binary system exists in room-temperature quantum dots is a fundamental step toward their practical use in computing.

More research is required, however. Atac Imamoglu, a professor of physics and of computer and electrical engineering at the university and principal investigator in the study, said that how quickly the dots turn on and off remains unknown. "Our experiments show that they do not blink faster than 1 µs."

The researchers plan to take what they have learned in this round of research, which they described in the Aug. 31, 2000, issue of Nature, and to pursue the development of high-repetition-rate, single-photon sources that operate at room temperature. The group also hopes to develop quantum cryptographic systems based on such sources.

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